Ventless equipment protection casing

ABSTRACT

Equipment, particularly of an electrical nature, is protected against internal explosion and flame hazard by enclosing the equipment and separating the equipment space within the enclosure from an expansion space in the enclosure by a flame arrester. As an alternative, the expansion space can be defined by a body of porous foamed material in the enclosure.

United States Patent I Palmer [54] VENTLESS EQUIPMENT PROTECTION ING Inventor: Kenneth Norman Palmer, Boreham Wood, England Assignee: National Reserch Development Corporation, London, England Filed: May 7,1970

Appl. No.; 35,522

[30] Foreign Application Priority Data May 14, 1969 Great Britain ..24,633/69 US. Cl. ..310/88, 220/88, 310/44, f 310/89 Int. Cl. ..l'l02k 5/22 Field of Search ..310/88, 44, 89, 273; 220/88;

References Cited UNITED STATES PATENTS 2/1971 Ashfordetalu, ..310 /88X 1 Och 17,1972

3,394,843 7/1968 Grady et a1. ..220/88 3,434,336 3/1969 I-Iarr ..220/88 X 2,618,540 11/1952 Teti ..220/88 1,007,828 11/1911 Webb .....220/88 2,743,035 4/1956 Fogarty ..220/88 FOREIGN PATENTS OR APPLICATIONS I 383,374 1 1/1932 Great Britain Primary Examiner.l. D. Miller Assistant Examiner-B. 'A. Reynolds Attorney-Cushman, Darby & Cushman [57] ABSTRACT Equipment, particularly of an electrical nature, is protected against internal explosion and flame hazard by enclosing the equipment and separating the equipment space within the enclosure from an expansion space in the enclosure by a flame arrester. As an alternative, the expansion space can be defined by a body of porous foamed material in the enclosure.

10 Claims, 4 Drawing Figures Pmmiunm 17 m: V

' All! IIIIIIIINHP 1. VENTLESS EQUIPMENT PROTECTION CASING This invention concerns equipment protection and more particularly the protection of equipment from the results of internal explosion and associated flame.

The traditional approach to such protection involves the use of casings which are rigorously defined as regards strength, openings to atmosphere, and so on. For example, British Standard Specification No. 229 which is relevant to this subject, requires that a flame-proof equipment casing be strong enough to contain an internalexplosion pressure of the order of I p.s.i., and also specifies the clearances, such as those around shafts projecting from the casing, which must be obtained to prevent the passage of flames. However, such aspecification is disadvantageous in adding significantly to the weight and cost of equipment.

A more recent approach to flame proofing has involved the use of so-called flame arresters. A flame arrester consists basically of a metal mesh or other porous material which will allow the passage of gas therethrough while preventing the passage of flame. Such an arrester is used where flammable gases may be present to vent an equipment casing to atmosphere. Then, if ignition of the gas should occur within the casing, gaseous products of the explosion can escape, while the flame is prevented from propagating beyond the casing where further explosion and fire could occur. Again this approach is not wholly satisfactory since the flame arrester will permit ingress of dust, corrosive gases, water orother foreign matter to the equipment, and can itself be rendered less effective unless frequently checked and cleaned. This difficulty can be reduced to a certain extent by the provision of acover for the flame arrester which cover opens in response to a rise of pressure within the associated casing. However, it will be appreciated that this'still leads to a requirement for frequent checking to ensure that the cover is operable to open, and a problem still exists from ingress of foreign matter.

An object of the present. invention is to reduce the above' difficulties of existing techniques-To this end it is proposed, in accordance with the present invention in a more general aspect, that flame arresters be internally located in equipment enclosures. Direct access to atmosphere is not then required in the event of an internal explosion and it is consequently simpler to take account of undesirable ingress of foreign matter. Such equipment is therefore suitable for use under arduous industrial conditions.

The invention will normally be put into effect by mounting a flame arrester at the entrance of a hollow vessel of such shape and volume that it will fit into the interior of an effectively closed equipment casing, or form an extension to close a casing which is otherwise open. For this purpose the normal or previous design of a casing-may have to be modified so that a vessel of adequate volume can be inserted or added. Such modification may also be desirable to reduce the free enclosed volume which is to be protected, that is to say the total enclosed free volume less the volume of the vessel.

The function of the vessel is firstly to act as a reservoir capable of taking up, without the development of excessive pressure, explosion gases driven into it through the flame arrester. Secondly, the vessel can serve to reduce or minimize the enclosed space which requires protection. The vessel may be of any convenient shape, providing that its volume is adequate to ensure an acceptably low explosion pressure.

' While it may be appropriate to use a vessel as discussed above, this is not essential; If there is sufficient free space within a casing, it may be possible to fit a flame arrester of suitable shape to separate that space into appropriate proportions 'as between regions in which there is and is not risk of explosion. Also flame arresters can be fitted as, or in, partition walls-of an equipment constructed as a combination of individual sections as is often the case with controlpanel structures on a rack frame. Naturally, in this last case, the flame arresters should not be in the external walls of the overall assembly.

The flame arrester is preferably of a metal or other material having a good thermal conductivity. This is advantageous in that explosion gases are cooled on passing through the arrester with resultant reduction in pressure.

The more conventional form of expanded or other mesh from metal flame arrester material is well suited to use in the present invention, although the recently developed porous foamed metal materials may prove equally useful. Indeed, the latter material affords the additional possibility of providing an expansion space in the form of a block of material within an equipment enclosure, rather than by use of a flame arrester partition between the equipment space and expansion space in such an enclosure as discussed above.

It will be appreciated, of course, that this foamed material will have a pore size which permits the passage of gas but not flame. Such a pore size will normally be at least of the order of 45 pores to the linear inch.

It is useful to illustrate the effectivenessof the invention by way of example. Explosion of a 4 percent by volume propane/air mixture within an enclosed onethird cu. ft. volume will produce a maximum pressure of about p.s.i. If this mixture is exploded in the same volume but vented into a vessel of l cu. ft. volume by way of a flame arrester which effects no significant cooling, the maximum pressure would be about 25 p.s.i. Tests carried out with this latter arrangement, but using a metal arrester, in fact resulted in a pressure of only 7 p.s.i. In another test using the same volumes with a cooling arrester, a faster burning, 6.5 percent by volume, ethylene/air mixture was exploded to produce a pressure of about 9 p.s.i. Naturally, if the 3:1 ratio of enclosure-to-vessel ratio inthe above examples were increased, the resultant explosion pressure would be correspondingly decreased.

For further clarification of the present invention, the same is illustrated by way of example with reference to the accompanying drawings, in which:

FIG. 1 schematically illustrates one embodiment of the invention,

FIG. 2 similarly illustrates a modification of FIG. 1 including a block form flame arrester,

FIG. 3 illustrates another embodiment of the invention, and

FIG. 4 illustrates a modification of FIG. 3.

The embodiment of FIG. 1 comprises a first enclosure part or casing 1 housing equipment 2 such as elec-. trical instruments, and a second housing part or lid 3 of panded or foamed metal 6 is located between. the casing and lid toserve as a flame arrester separating the free space 7 within the casing from that, 8, within the lid.

From the above more general discussion it will be ap-' preciated that the space 8 will normally be larger than the space 7.

FIG. 2 illustrates-a modification of FIG. 1 in which the flame arrester of partition form is replaced by a block of porous foamed metal 9 serving to substantially fill the lid space 8. The block 9 can be located in any suitable manner, such as by adhesive or other bonding into the lidspace, or by provision of a solid rim forentrapment between'the casing and lid rims, for example, whereby the .block is permanently or separably secured in place.

, The free space within the block 9 should, of course, be similar to the space 8 .in FIG. 1, so that the total volume of the block will normally be larger than space 8 and involve an appropriately larger lid.

The embodiment of FIG. 3 shows an electric motor or the like, having a casing 10 housing an annular stator 11 disposed around a rotor 12 from which a shaft 13 projects through the casing. The shaft passes through a bearing 14 in flame-proof manner so that the casing is effectively closed for the present purpose.

In accordance with the invention, a secondary enclosure 15 of annular form is located around the shaft within the casing to define and separate an expansion space 16 relative to the remaining free space 17 in the casing. The secondary'enclosure is partly formed by an annular area 18 of expanded or foamed metal facing axially inwardly relatively to the rotor.

The sameconsiderations as above regarding the proportionate volumes of spaces 16 and 17 apply in this instance. Also, the enclosure 15 can be replaced by an annular block 19 of porous foamed metal conveniently sited in the motor casing and cap 10a as indicated by FIG. 4.

As is apparent from the above discussion, the present invention is particularly applicable to situations where equipment is used under arduous industrial conditions and wherea lack of protection, should ignition occur within the equipment, could result in fire or explosion. Typical of the sort of equipmentto be protected is electrical equipment and equipment having moving parts with risk of sparking or other ignition. A prime example of such equipment is presented by electric motors which constitute one of the potentially hazardous items more commonly employed in combustible atmospheric conditions.

The advantages of the invention are also apparent from the introductory discussion, namely, the absence of a severe requirement for heavy and costly casings and enclosures, and reduced difficulty with ingress of foreign matter and the associated need for frequent inspection.

lclaim: V v, 1. A flame-proof casing for equipment, such as an electric motor, which may emit explosion and combustion gases during usage, said casing including:

exterior wall means forming a ventless enclosure,- barrier means within the ventless enclosure, dividing the interior of the ventless enclosure into two separate compartments, being respectively, an equipment receiving compartment. and an expansion chamber for explosion and combustion gases; said barrier means being so positioned that the free space in the expansion chamber exceeds the free space, defined as the space unoccupied by equipment, in the equipment receiving compartment when such equipment is received therein; the barrier means including surface means commu nicating between the two separate compartments.

and being permeable to explosion and combustion gases, said surface means being constructed of flame-arresting, heat abstracting material.

2. The flame-proof casing of claim 1 wherein said expansion chamber is filled with porous metallic sponge and said barrier means surface means is constituted by an exterior peripheral portion of said porous metallic sponge, said free space in the expansion chamber being defined at least in part within said porous metallic sponge.

3. The flame-proof casing of claim 2 wherein said exterior wall means is divided into two opposed, cupped sections, each having peripheral flange means extending therearound, the flange means lying adjacent one another and being adapted to be held together to maintain the casing in a closed condition.

4. Apparatus comprising a flame-proof, ventless casing having equipment located in a first part of the internal space thereof, a second part of said internal space serving as anexpansion chamber for explosion and combustion gases, a barrier separating said first and second parts, and a gas permeable flame arrester of heat abstracting material forming at least part of said barrier to cool and permit passage of said gases from said first part to said second part.

5. Apparatus according to claim 4 wherein said flame arrester fills said second part and the free space voids therein serve as said expansion chamber.

6. Apparatus according to claim 4 wherein the free space in said first part when occupied by said equipment is less than the free space in said second part including the voids in said flame arrester. v

7. Apparatus according to claim 4 wherein 'said flame arrester comprises a body of porous foamed metal.

8. Apparatus according to claim 7 wherein said metal has a pore size at least of the order of 45 pores to the linear inch.

9. Apparatus according to claim 4 wherein said flame arrester comprises a body of mesh farm metal.

10. Apparatus according to claim 4 wherein said equipment comprises an electric motor, and said casing has a removable end cap in which said flame arrester is sited. 

1. A flame-proof casing for equipment, such as an electric motor, which may emit explosion and combustion gases during usage, said casing including: exterior wall means forming a ventless enclosure; barrier means within the ventless enclosure, dividing the interior of the ventless enclosure into two separate compartments, being respectively, an equipment receiving compartment and an expansion chamber for explosion and combustion gases; said barrier means being so positioned that the free space in the expansion chamber exceeds the free space, defined as the space unoccupied by equipment, in the equipment receiving compartment when such equipment is received therein; the barrier means including surface means communicating between the two separate compartments and being permeable to explosion and combustion gases, said surface means being constructed of flame-arresting, heat abstracting material.
 2. The flame-proof casing of claim 1 wherein said expansion chamber is filled with porous metallic sponge and said barrier means surface means is constituted by an exterior peripheral portion of said porous metallic sponge, said free space in the expansion chamber being defined at least in part within said porous metallic sponge.
 3. The flame-proof casing of claim 2 wherein said exterior wall means is divided into two opposed, cupped sections, each having peripheral flange means extending therearound, the flange means lying adjacent one another and being adapted to be held together to maintain the casing in a closed condition.
 4. Apparatus comprising a flame-proof, ventless casing having equipment located in a first part of the internal space thereof, a second part of said internal space serving as an expansion chamber for explosion and combustion gases, a barrier separating said first and second parts, and a gas permeable flame arrester of heat abstracting material forming at least part of said barrier to cool and permit passage of said gases from said first part to said second part.
 5. Apparatus according to claim 4 wherein said flame arrester fills said second part and the free space voids therein serve as said expansion chamber.
 6. Apparatus according to claim 4 wherein the free space in said first part when occupied by said equipment is less than the free space in said second part including the voids in said flame arrester.
 7. Apparatus according to claim 4 wherein said flame arrester comprises a body of porous foamed metal.
 8. Apparatus according to claim 7 wherein said metal has a pore size at least of the order of 45 pores to the linear inch.
 9. Apparatus according to claim 4 wherein said flame arrester comprises a body of mesh farm metal.
 10. Apparatus according to claim 4 wherein said equipment comprises an electric motor, and said casing has a removable end cap in which said flame arrester is sited. 